HTTPS credentials rejected on Win7/IE8

Whenever I access *any* HTTPS site with a pop-up credentials window, my credentials get rejected, even after I clean my password vault. Is anyone else experiencing this?

Fred

What do you mean by "*any*"? Are they internal to your network? External? Did you try using compatibility view?

They're external sites of companies that I work for and access from home. The sites are up and running, as I can access them from my Vista-based machine. What happens is that my credentials simply get rejected.